how to modify blender to have real world particle physics?
Physics and particles are a tool to make movies. Not much else. They are intended to show how a steam engine works or a flock of birds in the distance. Force fields are meant to blow a smoke text away. Their job is to make stuff look good. They do not have the scope (yet) of being a physically accurate simulation of real world forces. 3D animation is the art of faking it. 

When I was doing my little solar system I didn't even try the physics, I just coded a bit of python gravity myself. Also not physically accurate (no need) but I got some nice elliptical orbits. Managed some gravity slingshots, too.

So either you really need to work on the code or you might get away with python or python with C/C++ help, depending on the performance needs. Changing the source code of course means one of three outcomes: You need to merge your code every time a new version comes out, you get it committed and it becomes a part of the official release or you are stuck with a Blender version that slowly gets old.

At the last Blender Conference there was a talk about simulating quite a few million blood cells with a super computer. So there's some fancy stuff possible if you're determined.

If you want these features, start to make them happen.